The present invention relates to an apparatus for detecting focus conditions of an imaging optical system in a camera, microscope or the like.
A technique has been disclosed in, for example, Japanese Patent Laid-open Nos. 60,645/73 and 95,221/77, by which light flux transmitted through the right half part of the exit pupil of an objective lens and light flux transmitted through the left half part of the exit pupil are separated by a proper separation means, and photoelectrically converted into signals having waveforms corresponding to respective images, and phase shifts of both signals are compared with each other thereby obtaining signals representing forwardly- and backwardly-defocused conditions and the in-focused condition. The former utilizes a vibrating slit as a light flux dividing means resulting in the necessity of mechanically movable components and the latter must provide a relay lens at the rear of a predetermined focal plane of the objective lens; the latter requiring comparatively wide space so that, in any case, it is impossible to derive, with adequate high correlation, the photoelectrically converted output of light fluxes transmitted through two regions defined by a plane including the optical axis of the objective lens.
Japanese Patent Laid-open No. 159,259/79 discloses a focus condition detecting apparatus in which a plurality of microlens arrays are provided instead of a relay lens, with a plurality of paired light receiving elements corresponding to respective microlenses, and these paired light receiving elements are arranged in an array corresponding to the microlens array. In this focus condition detecting apparatus the light quantity distribution of light flux transmitted through one region of the objective lens defined by a plane including the optical axis of the exit pupil and the light quantity distribution of light flux transmitted through the other region of the objective lens are compared with a ratio of 1:1 for respective light receiving element pairs to any position of the objective lens. The position of the objective lens at which two light quantity distributions completely coincide with each other is referred to as the in-focus position. In such an apparatus the paired light receiving elements corresponding to respective microlenses are arranged in such a manner that light flux transmitted through one region of the exit pupil of the objective lens and light flux transmitted through the other region of the exit pupil are incident upon the paired light receiving elements in a completely separated manner. When the opened angle of major light ray of both light fluxes incident upon the paired light receiving elements is large and thus the defocused amount becomes large, as in the case of utilizing an imaging lens or the like having a large extension amount thereof such as a single-lens reflux camera whereby lateral shift becomes large, the image portion necessary for obtaining correlation is shifted from the light receiving element. This results in the impossibility of detecting focus condition with high precision and the incapability of detecting the focus condition. As a method of preventing such disadvantages, a light receiving element having a large light receiving area has been provided; however, this results in an increase of manufacturing cost of light receiving elements because of a decrease in yield and the necessity for excess packaging space, and, in any event, enlargement of the light receiving area is limited because of the relative position of paired light receiving elements.